Window treatment accessory



FIG. 1 is an environmental perspective view with the broken line showing of a partial curtain, curtain rod and bracket are for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a front view thereof (the rear view, the top plan view and the bottom plan view being mirror images of the front view);

FIG. 3 is a right side view thereof; and,

FIG. 4 is a left side view thereof. 

The ornamental design for a window treatment accessory, as shown and described in the drawings. 